Heretofore it has been known to provide nozzle means, for the breast box of a paper-making machine, wherein the nozzle means comprises an opening or gap, through which pulp stock is flowed, and wherein such opening or gap is comprised of a lower disposed lip or lip surface and an upper disposed lip or lip surface. Further, in such prior art structures a shutter means or member, operatively carried as at a downstream position of such upper lip, can be moved, generally, upwardly and downwardly as to thereby selectively determine the effective height of such opening or gap. Such reciprocal movement of the shutter is usually accomplished as by a plurality of threaded spindles which operatively engage the shutter and which are operated as by, for example, handwheels or the like.
The thusly selected width of the gap or opening of the breast box nozzle therefore determines the thickness of the stream of pulp stock emerging from the nozzle.
In such arrangements the shutter projects downwardly some amount into the stream of pulp stock and consequently experiences a considerable pressure thereagainst, at the upstream side of the shutter, applied by such flowing stream of pulp stock. Such pressure causes some degree of deflection in the shutter which, in turn, results in uncontrolled variations in the effective width of the nozzle gap causing defects in the resulting paper web.
The prior art has been aware of the problem of such undesired shutter deflection, and the defects in the resulting paper web, and has attempted to solve such problem as by, for example: significantly increasing the thickness of the shutter, which is usually constructed as in the form of a steel straight-edge member; dividing the shutter member into separate sections which are, generally, functionally aligned as to span the entire longitudinal length of the nozzle gap or opening; and providing for a more sensitive adjustment of the threaded adjustment spindles as to thereby, hopefully, offset the effects of the upstream created pressure on the shutter means and eliminate the resulting surface-weight fluctuations occurring in the subsequent paper web, paper, strips and the like. None of such prior art attempts has proven to be successful and such defects and surface-weight fluctuations of the paper web and paper product continued.
In the embodiments of breast box nozzles heretofore employed, a support is provided as to lie directly against, what may be termed, the downstream side of the straight-edge type of shutter. Such support was intended to hold the shutter in such a way as to prevent deformation of the shutter due to the upstream pressure created by the flow of pulp stock. However, despite efforts, the prior art has been unable to manufacture a shutter so dimensionally accurate as to assure that the said support would always rest flush, throughout its length, against the shutter member. The manufacturing tolerances, in order to attain the required flatness, surface parallelism, etc., are extremely critical (and for all practical purposes unattainable) since the slightest undesired curvature or warping of the shutter edge exerts a damaging influence on the quality of the stream of pulp stock and the resulting paper web. Consequently, because of the unattainable dimensional accuracy, the said support, instead of lying flush (along its entire functional length) against the shutter actually engages the shutter only at what amounts to spaced points. Such, of course, only further encouraged the undesired bowing or deflection of the shutter. Even with manufacture to close tolerances, due to the considerable temperature fluctuations arising in the area of the shutter, internal and applied material stresses are released which, again, result in the non-flush contact as between the shutter and said support.
Such problems of the prior art have been overcome by the structure disclosed and claimed in U.S. Pat. No. 4,326,916 dated Apr. 27, 1982. Briefly, said Letters Patent discloses a breast box nozzle assembly comprising a support member and elastomeric means operatively interposed between the support member and a downstream side of the associated shutter whereby the elastomeric means is effective to react against the support member and apply a reacting force as a counter pressure to the downstream side of the shutter to thereby hold the shutter against its cooperating mounting surface while still permitting the shutter to be adjustably moved in either of two directions of travel.
A problem has been discovered with the structure of said Letters Patent. That is, after prolonged use there is the possibility that the elastomeric means may become damaged. More particularly, in the preferred embodiment of the structure of said Letter Patent the elastomeric means comprises a hose-like or tube-like means which is internally pressurized as to thereby act against the shutter. Further, a structural clearance or gap exists as between the shutter and a juxtaposed end of the associated support member against which the elastomeric means reacts. In the prolonged use of such a structure there is a possibility that the elastomeric means will become damaged as at an area where it is urged toward or pressed into such gap between the shutter and said associated support member. Such a possibility of damage increases especially when thick paper grades are being produced and the shutter is moved as to provide a correspondingly wide opening thereby requiring a considerably greater movement of the shutter, relative to elastomeric means, and a greater tendency to frictionally force the elastomeric means into said gap.
The invention as herein disclosed and claimed is primarily directed to an improvement whereby the possibility of such damage occurring to said elastomeric means is eliminated or at least greatly minimized even though the shutter may have to be adjustably moved a relatively long distance.